In an automotive environment many electrical hazards exist. For example, various automotive devices and sub-systems can generate electromagnetic interference, electrical disturbances, such as electrostatic discharges and others directly or indirectly into the supply voltage wiring.
In the automotive industry, in particular recently the external connector VBAT test has been introduced. Each USB compliant port has generally 4 connection lines Vbus, Gnd, D+ and D−. A relatively high voltage may be connected to any of the connection ports. In a three-port USB system this would require to protect 12 separate connection lines. A user may have no economical solution to protect these 12 lines in the 3×USB micro connector.
Since there are multiple ports and multiple contacts per port for this test, the only common connection to isolate this test condition is to isolate the entire board ground through a MOSFET switch. Initially a single MOSFET isolation scheme has been tested whereby it was attempted to isolate the entire module from ground. Unfortunately, due to interaction and interconnection of the three functional sections on the module (in one embodiment, a DC-DC converter, USB HUB component and other components), this solution does not work. A similar approach could be used to protect many ports associated with an MCU or any analog, digital, or interface device. By detecting excess current in the ground return of said device and “clamping” the outputs of said device to its local ground connection, the possibility exists to protect the device from external voltage exposure.